That force can have two separate components. It can pull matter "vertically," by which we mean perpendicularly to the Earth's surface. And it can also pull things "horizontally" — i.
Now, the spot on the globe that sits right beneath the moon at any given time is called the sublunar point. Meanwhile, the spot on the other side of our planet that is directly opposite the sublunar point is known as the antipodal point.
It's no coincidence that the ocean bulges are highest right over those two spots. At the sublunar point and the antipodal point, the moon's gravitational pull lacks a horizontal component — something that is also missing at the two corners of the world that are located 90 degrees away from these spots.
Those four areas are unique in that regard; every other location on Earth experiences a horizontal force that pushes water molecules in the ocean toward either the sublunar point where the moon's gravitational force is at its strongest or the antipodal point where the moon's gravitational pull is at its weakest.
This is why the ocean bulges up over those two areas. Once every 24 hours, Earth completes a full rotation around its axis. During this process, any given spot on the planet's surface like, say, Long Island or Australia will pass right through both of those ocean bulges.
So — in most areas — when your home is directly under a bulge, the local tide should be high. But as it enters the space between the bulges, the tide in your area should get lower. This isn't always the case, as you'll learn next. For now, let's discuss another factor that influences our tides. The sun also exerts a gravitational pull on the oceans , but because our solar companion is further away, its effects on the tides are less pronounced than the moon's.
Still, the big ball of gas and plasma does noticeably enhance tidal bulges on a regular basis. He notes that this happens during two separate lunar phases: Full moons and new moons. Astronomers and Earth scientists refer to these plus-sized tides as spring tides.
Note that the name has nothing to do with the spring season; indeed, spring tides occur throughout the year. During spring tides, the "high" tides are really high and the "low" tides are unusually low.
Things get less extreme when the sun and moon sit at right angles to each other relative to Earth. Such an arrangement will produce a neap tide; a period in which the difference between high and low tides is minimal.
Brace yourself: Things are about to get even more complex. They're not associated with the Spring season at all as they occur every month. But no alliance can last forever. The three bodies soon fall out of alignment with each other, and seven days after a spring tide the Moon and the Sun are at 90 degree angles from each other. The alignment turns into a tug of war, and tides become unusually weak. That's known as neap tides. Let's say the Moon is above the Pacific Ocean. As the Earth rotates during the day, the bulge changes.
Most coastlines experience two bulges, or high tides, and two low tides a day. It's important to note that this all happens unevenly. The Earth isn't one giant ocean. Rocky land and beaches get in the way of all these tidal tugs, altering them in size and stature. So some places have large bulges while others are small.
The first bulge comes from the Moon being above an ocean. But on the other side of the world, the ocean is also bulging. Tidal force is differential force so it comes from differences in gravity over the Earth's surface. Here's how NASA describes it:. Tides also play a huge role in shipping.
Figure Water on the opposite side of the Earth is pulled least by the moon so the water bulges away from the moon. High tide occurs where the water is bulging.
Low tide occurs where it is not. How does the Moon affect the oceans? This is because the Earth is closer to the moon than the water on its far side. These two water bulges on opposite sides of the Earth aligned with the Moon are the high tides. Since ocean water is pulled higher in the areas of the two high tides, there is less water in between the two high tides. These areas are the low tides Figure The tidal range is the difference between the ocean level at high tide and the ocean at low tide Figure Some places have a greater tidal range than others.
High tides occur about twice a day, about every 12 hours and 24 minutes. Sometimes, the Sun and Moon are on opposite sides of the Earth while at other times, they are on the same side. Neap tides occur when the Earth, the Sun, and the Moon form a right angle, at first and last quarters for the Moon. The Sun is much larger than our Moon. It has a mass about 27,, times greater than the Moon. A very large object like the Sun would produce tremendous tides if it were as near to Earth as the Moon.
When both the Sun and Moon are aligned, the effect of each is added together, producing higher than normal tides called spring tides. Spring tides are tides with the greatest tidal range.
They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. The material that follows on tides was cut from Ocean Movements section under Coastal Processes.
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